A conventional heat sink for power module is disclosed in, for example, Patent Document 1. The heat sink for power module is made of aluminum or copper (the “aluminum” herein includes aluminum alloy other than pure aluminum and the “copper” includes copper alloy other than pure copper). A refrigerant passage in which cooling medium such as water flows is defined in the heat sink for power module. More specifically, the heat sink for power module has a laterally elongated rectangular cross section. In the heat sink, the refrigerant passage having a laterally elongated rectangular cross section is provided. Fins extending in an up-and-down direction are arranged in the refrigerant passage and increase the contact area with respect to the cooling medium.
An insulated circuit substrate on which power devices such as semiconductor chips are mounted is arranged at one surface of the heat sink for power module. Before the power devices are mounted, the structure is referred to as a substrate for power module including a heat sink for power module and an insulated circuit substrate.
The insulated circuit substrate includes, for example, a wiring layer formed of aluminum, an insulated substrate that is formed of insulating ceramic and joined to the wiring layer, and a heat radiating layer that is formed of aluminum and joined to the insulated substrate. When the substrate for power module is used, power devices such as semiconductor chips are mounted on the wiring layer. A heat radiating plate that is formed of aluminum and sized at 3 to 10 mm is provided between the insulated circuit substrate and the heat sink for power module.
The conventional heat sink for power module, which is configured as above-described, forms a power module when an insulated circuit substrate on which power devices such as semiconductor chips are mounted is provided at one surface of the heat sink. The power module may be used in an inverter circuit of a movable body such as a hybrid vehicle, which employs an electric motor as one of its drive sources. In this case, the power module adjusts the power supplied to the electric motor or the like in correspondence with the operating state of the movable body. The power module transmits intense heat generated by the power devices to the heat sink for power module through the wiring layer, the insulated substrate, the heat radiating layer, and the heat radiating plate. The heat is then dissipated by the cooling medium flowing in the refrigerant passage.
However, the conventional heat sink for power module has the following problem with regard to the efficiency of transmission of the intense heat generated by the power devices to the cooling medium, which flows in the refrigerant passage, from the refrigerant passage or the surfaces of the fins.
Specifically, in the above-described conventional heat sink for power module, the fins that extend in the up-and-down direction are provided in the refrigerant passage in order to increase the contact area with respect to the cooling medium. However, regardless of the fins, the temperature of the cooling medium becomes higher toward the area thermally closer to the power devices. The distribution of the temperature of the cooling medium in the heat sink for power module thus becomes nonuniform. This limits effective cooling performance of the cooling medium to a certain level and lowers the heat dissipating efficiency. As a result, in the heat sink for power module, transmission of the heat from the inner surfaces of the refrigerant passage or the surfaces of the fins to the cooling medium is hampered. This makes it difficult to further improve the heat dissipating performance.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-86744